全文获取类型
收费全文 | 1617篇 |
免费 | 94篇 |
专业分类
林业 | 36篇 |
农学 | 34篇 |
基础科学 | 16篇 |
158篇 | |
综合类 | 296篇 |
农作物 | 76篇 |
水产渔业 | 101篇 |
畜牧兽医 | 898篇 |
园艺 | 36篇 |
植物保护 | 60篇 |
出版年
2021年 | 16篇 |
2019年 | 27篇 |
2018年 | 16篇 |
2017年 | 26篇 |
2016年 | 30篇 |
2015年 | 26篇 |
2014年 | 22篇 |
2013年 | 124篇 |
2012年 | 48篇 |
2011年 | 78篇 |
2010年 | 41篇 |
2009年 | 31篇 |
2008年 | 64篇 |
2007年 | 49篇 |
2006年 | 55篇 |
2005年 | 47篇 |
2004年 | 58篇 |
2003年 | 48篇 |
2002年 | 52篇 |
2001年 | 51篇 |
2000年 | 45篇 |
1999年 | 25篇 |
1998年 | 16篇 |
1997年 | 16篇 |
1996年 | 15篇 |
1995年 | 21篇 |
1994年 | 14篇 |
1993年 | 13篇 |
1992年 | 36篇 |
1991年 | 27篇 |
1990年 | 22篇 |
1989年 | 27篇 |
1988年 | 30篇 |
1987年 | 25篇 |
1986年 | 30篇 |
1985年 | 22篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1981年 | 18篇 |
1980年 | 22篇 |
1979年 | 21篇 |
1978年 | 23篇 |
1976年 | 16篇 |
1974年 | 20篇 |
1973年 | 20篇 |
1972年 | 16篇 |
1971年 | 16篇 |
1970年 | 15篇 |
1969年 | 20篇 |
1966年 | 11篇 |
排序方式: 共有1711条查询结果,搜索用时 953 毫秒
141.
Fong DD Stephenson GB Streiffer SK Eastman JA Auciello O Fuoss PH Thompson C 《Science (New York, N.Y.)》2004,304(5677):1650-1653
Understanding the suppression of ferroelectricity in perovskite thin films is a fundamental issue that has remained unresolved for decades. We report a synchrotron x-ray study of lead titanate as a function of temperature and film thickness for films as thin as a single unit cell. At room temperature, the ferroelectric phase is stable for thicknesses down to 3 unit cells (1.2 nanometers). Our results imply that no thickness limit is imposed on practical devices by an intrinsic ferroelectric size effect. 相似文献
142.
143.
144.
145.
Daniel R. Block Michael Thompson Jill Euken Toni Liquori Frank Fear Sherill Baldwin 《Agriculture and Human Values》2008,25(3):379-388
Engagement happens when academics and non-academics form partnerships to create mutual understanding, and then take action
together. An example is the “value web” work associated with W. K. Kellogg Foundation’s Food Systems Higher Education–Community
Partnership. Partners nationally work on local food systems development by building value webs. “Value chains,” a concept
with considerable currency in the private sector, involves creating non-hierarchical relationships among otherwise disparate
actors and entities to achieve collective common goals. The value web concept is extended herein by separating the values
of the web itself, such as the value of collaboration, from values “in” the web, such as credence values associated with a
product or service. By sharing and discussing case examples of work underway around the United States, the authors make a
case for employing the value webs concept to represent a strategy for local food systems development, specifically, and for
higher education–community partnerships, generally.
Daniel R. Block is an associate professor of geography and coordinator of the Frederick Blum Neighborhood Assistance Center at Chicago State University. His current research focuses on food access issues in urban environments, particularly in Chicago. Michael Thompson is an assistant professor at Oregon State University, and a Seafood and Fisheries specialist for Oregon Sea Grant Extension. Primary areas of research include fisheries management, seafood quality/handling, and seafood product development. Jill Euken is an industrial specialist for biobased products for Iowa State University Extension/CIRAS, and deputy director, ISU Bioeconomy Institute. She was part of the steering team for the Iowa Value Chain Partnership for Sustainable Agriculture and led the Bioeconomy Working Group. Toni Liquori is a nutritionist, teacher and food activist with a long time interest in the design, implementation, and evaluation of school-based intervention programs and coalition building for activism around food related issues, as well as teaching and training in public health. Frank Fear is senior associate dean, College of Agriculture and Natural Resources; and professor, in the Department of Community, Agriculture, Recreation and Resources Studies; and Senior Outreach Fellow at Michigan State University. He is lead author of Coming to Critical Engagement (University Press of America, 2006), an analysis of the engagement movement in higher education; and recently completed two terms as president of the Greater Lansing Food Bank. Sherill Baldwin is ecology director at Mercy Center at Madison, Connecticut, a spiritual retreat and conference center. She previously provided consulting services to CitySeed, Inc. in New Haven (CT) and to Frank Fear and the W. K. Kellogg Foundation for a community learning project related to sustainable food systems. She has an MS in Resource Development from Michigan State University and a BA in Solid Waste Management from the University of Massachusetts. 相似文献
Daniel R. BlockEmail: |
Daniel R. Block is an associate professor of geography and coordinator of the Frederick Blum Neighborhood Assistance Center at Chicago State University. His current research focuses on food access issues in urban environments, particularly in Chicago. Michael Thompson is an assistant professor at Oregon State University, and a Seafood and Fisheries specialist for Oregon Sea Grant Extension. Primary areas of research include fisheries management, seafood quality/handling, and seafood product development. Jill Euken is an industrial specialist for biobased products for Iowa State University Extension/CIRAS, and deputy director, ISU Bioeconomy Institute. She was part of the steering team for the Iowa Value Chain Partnership for Sustainable Agriculture and led the Bioeconomy Working Group. Toni Liquori is a nutritionist, teacher and food activist with a long time interest in the design, implementation, and evaluation of school-based intervention programs and coalition building for activism around food related issues, as well as teaching and training in public health. Frank Fear is senior associate dean, College of Agriculture and Natural Resources; and professor, in the Department of Community, Agriculture, Recreation and Resources Studies; and Senior Outreach Fellow at Michigan State University. He is lead author of Coming to Critical Engagement (University Press of America, 2006), an analysis of the engagement movement in higher education; and recently completed two terms as president of the Greater Lansing Food Bank. Sherill Baldwin is ecology director at Mercy Center at Madison, Connecticut, a spiritual retreat and conference center. She previously provided consulting services to CitySeed, Inc. in New Haven (CT) and to Frank Fear and the W. K. Kellogg Foundation for a community learning project related to sustainable food systems. She has an MS in Resource Development from Michigan State University and a BA in Solid Waste Management from the University of Massachusetts. 相似文献
146.
147.
Chemical analyses of morphologically preserved organic matter in a Carboniferous coal ball reveal that the material is coalified to a rank approximately equal to that of the surrounding coal. Hence, the plant tissues in the coal ball were chemically altered by coalification processes and were not preserved as peat. 相似文献
148.
149.
Oxygen and hydrogen isotopic ratios in plant cellulose 总被引:2,自引:0,他引:2
The variations of the D/H and (18)O/(16)O ratios of nonexchangeable hydrogen and oxygen in plant cellulose reveal systematic differences between terrestrial plant groups. The slope of deltaD versus delta(18)O of cellulose from a variety of aquatic plants is close to 8 (the meteoric water value), while the slope for a number of terrestrial species is greater than or equal to about 24. Two models involving incorporation of CO(2) and H(2)O into cellulose precursors are proposed to account for these differences. Effects of evaporative transpiration on the isotopic composition of water in leaves are measured and discussed in the context of these models. 相似文献
150.